Blind Period Search gamma-ray pulsar by Fermi-LAT. F. Giordano Dipartimento Interateneo di Fisica and INFN Sez. Bari for the Fermi LAT collaboration. Where we were: the EGRET Pulsars. Vela, Crab & Geminga are the brightest sources in the Gamma-ray sky
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Dipartimento Interateneo di Fisica
INFN Sez. Bari
Fermi LAT collaboration
Vela, Crab & Geminga are the brightest sources in the Gamma-ray sky
Their Flux for E>100MeV 10-5÷10-6ph/cm2s
Vela (16 days)
PSR B1951+32 (25 days)
Geminga (16 days)
Crab (16 days)
PSR B1055-52 (25 days)
PSR B1706-44 (25 days)
1/10th true rate
The Geminga candidates
1. Radio-quiet gamma-ray sources list generated pre-Launch, with very accurate source locations from other wavelengths.
a. 3EG J1835+5918 (possibly the “next Geminga”)
b. CTA1 (recently published in Science)
c. Compact objects of Pulsar Wind Nebulae (PWNe)
d. Milagro sources (e.g. MGROJ2019+37)
2. Fermi-LAT sources – a list of gamma-ray sources generated post-Launch with a Fermi localization
The spin parameters (frequency, spin-down) are unknown, so to resolve the phase plot, a search over f, df/dt parameter space has to be implemented to find the timing solution.
1. Gamma-ray photon data is exceptionally sparse (103104 photons per yr ).
2. Such long datasets make fully coherent methods like FFTs require large numbers of fdot trials to prevent smearing of the signal. This large number of trials would also greatly reduce the significance of the signal.
3. FFTs of this magnitude require large amounts of memory:
1 month @ 64 Hz = 331 million bins = 5.3 GB of memory!
4. If the pulsar were to glitch (suddenly change its frequency), then the signal power would diminish greatly.
Periodicity in photon arrival times will also show up in differences of photon arrival times.
Time differences cancel out long term phase slips because differencing starts the "clock" over (and over, and over...)
Despite the reduced frequency resolution (and therefore number of bins), the sensitivity is not much reduced because of a compensating reduction in the number of fdot trials
Science, Volume 322, Issue 5905, pp. 1218- (2008).
CTA 1 pulsar (2 cycles, P=315.86 ms)
P 315.8 ms
3EG J1826-1302 (Eel)
3EG J1420-6038 (Rabbit)
1 MGRO + 2 new Fermi Sources
Blind search pulsars
B Strength (Gauss)
- 13 new (potentially radio-quiet) gamma-ray pulsars have been discovered in 3 months of Fermi-LAT data
- 10 out of 13 of these blind period search pulsars have an EGRET source location (3EG). Since two-thirds of EGRET sources remain unidentified, and this is a good step in identifying them.
- These pulsars have an age distribution 10 kyr - 1.8 Myr and spin-down luminosity distribution: 1033 erg/s - 1036 erg/s
- These new pulsar discoveries will enable a population study of radio-quiet vs. radio-loud pulsars which will provide new information on the emission geometry in these sources and the galactic populations of these high energy emitters.
- Deep radio pulsar searches of the new gamma-ray only pulsars have begun, in order to get strong constraints on the radio luminosity.